The present invention relates to a method for the electrical purification and decontamination of liquids and to an apparatus for effecting same.
An apparatus according to the present invention can find application, in example, for supplying water to troops in the field, for supplying water to geological parties in remote regions, for supplying water to timber logging sites, radar stations, surface and sub-surface ships and other vessels, for supplying water to manned orbiting space stations; it can also be used in water preservation systems for the above-mentioned applications, as well as for the purification of water by removing radioactive and toxic substances in the chemical and chemico-pharmaceutical industry for the recovery of valuable substances, as well as for medico-biological purposes, such as preparation of pyrogenic water.
Known in the art is a method for the purification and decontamination of liquids a wherein the liquid is passed, sequentially or in parallel, through inter-electrode gaps formed by flat electrodes, with a constant or pulsating voltage in the range of from 3 to 30 volts.
Disadvantages of the above process resulting from a rather low field intensity, its uniformity and the quite character of the process hydrodynamics, reside in the deposition of an oxide film on the anode surface, the presence of a concentration polarization effect, deposit formation on the cathode, increasing equivalent resistance of the inter-electrode space, and the necessity of introducing an oxidizing agent to convert Fe(OH).sub.2 into Fe(OH).sub.3.
Another prior art method for the electric purification and decontamination of liquids comprises passing a liquid through a packed inter-electrode space, the packing being comprised of metal chips or other metal particles, arranged in layers separated from each other by porous diaphragms, the voltage across the electrodes being under 100 volts.
A disadvantage of the above-described method resides in that the porous diaphragm tends to become clogged with metal hydroxide due to a limited volume of flake removal, resulting in increased hydraulic resistance to the flow of liquid, with a considerable portion of the flow passing through the packing without taking part in the purification process, since the surfaces of the chips in the packing are in a state of mutual electrical contact.
According to another known method the liquid passes through the inter-electrode space formed by coaxially arranged cylinder electrodes, the voltage applied thereto being under 100 volts.
A disadvantage of the above method resides in low efficiency of dipolophoresis, due to low non-uniformity of the electric field another disadvantage is the decreasing efficiency of the process under increasing intensity of the electric field and concentration of suspended particles, due to intensive deposition of particles on the anode under the conditions of quiet hydrodynamics of the process.
Also known in the art is a method for the purification and decontamination of liquids by means of a high-voltage electric discharge wherein a liquid is subjected to the effect of electrical discharge, the voltage used being in the order of 10000-100000 volts, current over 100 amperes and pulse duration of from 0.1 to 100 microseconds, which results in heavy losses of electric power, the presence of reactance losses, unsatisfactory bactericidal effect, dangerous sounds, voltages and currents, as well as the formation of cancerogenic substances in the process of purification.
Also known in the art is an apparatus for effecting the purification and decontamination of liquids for realizing the first mentioned method, which apparatus comprises a coagulation chamber having electrodes in the form of flat plates. A disadvantage of the apparatus resides in a large anode surface and the impossibility of smooth adjustment of the inter-electrode space, which results in the formation of an oxide film on the surface of the anode, the appearance of concentration polarization, the formation of deposits on the cathode which increases equivalent resistance of the inter-electrode space, and the need to introduce an oxidizer for the purpose of converting Fe(OH).sub.2 into Fe(OH).sub.3.
The known apparatus for effecting the electric purification and decontamination of liquids realizing the above-mentioned method wherein packed electrodes are used in the form of a bank of cells separated from each other by porous diaphragms arranged between current-conducting electrodes, has disadvantages which reside in the fact that as the process proceeds the packed material tends to dissolve, which calls for the application of special devices for compressing the packed material and requires the current polarity to be changed.
There is also known an apparatus for realizing the above-mentioned method wherein use is made of cylindrical electrodes and the apparatus comprises a coagulation chamber with coaxial cylindrical electrodes.
A disadvantage of the apparatus resides in the fact that due to low non-uniformity of the electrical field of the inner large-diameter electrode, which reduces the value of dipolophoretic forces, independent of the charge of the particles, it is necessary to provide a pre-settler for removing large particles having a low electric charge.
There is also known an apparatus for the electric purification and decontamination of liquids for realizing the method and employing a high-voltage electrical discharge. In this apparatus the starting liquid flows through a coagulation chamber wherein at least two rod type electrodes are disposed, one of the rod-type electrodes is electrically insulated from the housing of the coagulation chamber by means of an insulator, the electrodes being disposed inside the housing in such a manner that their longitudinal axes lie in parallel planes, the distance between the planes being within the size of the inter-electrode space.
The electrodes in the apparatus are fixedly secured in the housing. Among the disadvantages of the apparatus are a large destruction of insulation of one of the electrodes, a low degree of utilization of the purification volume, the necessity of frequent replacement of one of the electrodes, and the need of having a very high-strength housing.